Abstract?An improved switch core principle is described which can be applied to a pulsewidth as short as 50 ns. The factors usually limiting switch core performance, such as pulse distortion due to low field strength, heat, and noise are eliminated by the use of long, thin permalloy needles. These needles can easily be provided with coils with a large number of turns and thus high field strengths can be applied. Because of its improved cooling properties and the fact that a permanent magnet bias can be used, the heat problem is greatly reduced . Finally, the permalloy material has such extremely good saturation properties that the noise figures are reduced in spite of the higher speed.